1. Field of the Invention
The present invention relates to a gel electrolyte, and in particular relates to the composition thereof and method for manufacturing the same.
2. Description of the Related Art
A photovoltaic cell is a photoelectric semiconductor chip that directly generates electric power by sunlight. When the chip is exposed to sunlight, it simultaneously outputs current and voltage. The photovoltaic cell is a so-called solar cell. The solar cell regenerates power in an environmental friendly way, as no harmful gases, such as carbon dioxide, is produced from the power generating process. Referring to material-types thereof, the solar cell can be classified into silicon-based solar cells, dye sensitized solar cells, organic solar cells, and the likes. The most important factor for solar cells is conversion efficiency. Recently, the highest conversion efficiency for silicon-based solar cells is 29% for a single crystal silicon (in laboratory), 24% for a poly crystalline silicon, and 17% for an amorphous silicon.
A dye sensitized solar cell (DSSC) has recently been disclosed. Different from conventional photovoltaic cells, the top substrate of the DSSC is usually glass or transparent flexible polymer foil. A transparent conductive oxide such as fluorine doped tin oxide (SnO2:F, FTO) or indium tin oxide (ITO) is formed on the glass. A porous layer of about 10 μm, such as nano-porous film composed of TiO2 particles having diameters of about 10 to 20 nm, is formed on the transparent conductive oxide. A dye such as a ruthenium polypyridyl complex is then coated on the above nano-porous film to form the so-called top substrate. The bottom substrate of the DSSC is usually glass or transparent and flexible polymer foil. In addition to the transparent conductive oxide such as an FTO layer on the glass, a platinum layer is coated on the FTO layer to catalyze the reaction of the electrolyte. An electrolyte including iodine compound is injected between the top and bottom substrates. The highest conversion efficiency of the DSSC is only about 10%, however, the process for manufacturing the DSSC is simple. Therefore, the production cost or required power per kilowatt-hour for DSSC is minimal.
A typical electrolyte of the DSSC is a liquid electrolyte with leakage problem. A gel electrolyte is not initially used, because of the difficulty in injecting gel into space between the top and bottom of the substrates. Thus, the liquid electrolyte is added polymerizable monomer and a corresponding initiator, and injected into the top and bottom of the substrates. Subsequently, the electrolyte is heated to polymerize and become gelled. However, this method often damages the photosensitive dye of the DSSC due to requirement for a high polymerization temperature, which decreases device performance.
Accordingly, a suitable gel electrolyte that can be formed under mild conditions in a solar cell is called for to reduce DSSC manufacturing costs.